A printing apparatus having the function of a printer, copying apparatus, facsimile apparatus, or the like, or a printing apparatus used as an output device for a composite electronic device or workstation including a computer, word processor, or the like prints an image on a printing medium such as a paper sheet or thin plastic plate on the basis of image information (including character information or the like). Such printing apparatuses can be classified by the printing method into an ink-jet type, wire dot type, thermal type, laser beam type, and the like.
Of these printing apparatuses, a printing apparatus of an ink-jet type (ink-jet printing apparatus) prints by discharging ink from a printing means (printhead) onto a printing medium. The ink-jet method is superior to other printing methods because the resolution can be easily increased and the ink-jet printing apparatus achieves high speed, quietness, and low cost. On the other hand, needs for color printing have grown, and many color ink-jet printing apparatuses have been developed. As a printhead constituted by integrating and arraying a plurality of printing elements for higher printing speed, the ink-jet printing apparatus uses a printhead in which ink orifices (nozzles) serving as an ink discharge portion and a plurality of liquid channels are integrated. To cope with color printing, the ink-jet printing apparatus generally comprises a plurality of printheads.
FIG. 1 shows the arrangement of a printer part when the printhead prints on a printing sheet surface. In FIG. 1, reference numerals 101 denote ink cartridges. The ink cartridges 101 are comprised of ink tanks which respectively store four color inks, i.e., black, cyan, magenta, and yellow inks, and a printhead 102 having orifices for discharging these inks. FIG. 2 shows orifices arrayed on the printhead 102 when viewed from the z direction. Reference numerals 201 denote orifices which are arrayed in the printhead 102. The orifices are openings at the ends of nozzles, and ink is discharged from the orifices by driving discharge means arranged in the orifices.
Referring back to FIG. 1, reference numeral 103 denotes a sheet supply roller which rotates in a direction indicated by an arrow in FIG. 1 to supply a printing sheet P in the y direction while holding the printing sheet P together with an auxiliary roller 104; 105, sheet feed rollers which feed a printing sheet and also hold the printing sheet P, similar to the rollers 103 and 104; and 106, a carriage which supports the four ink cartridges and moves them along with printing. When no printing is done, or printhead recovery operation or the like is performed, the carriage 106 stands by at a home position (h) represented by the dotted line in FIG. 1.
Before the start of printing, the carriage 106 at the position (home position) in FIG. 1 moves in the x direction upon reception of a printing start instruction, and printing is executed by a plurality of orifices 201 of the printhead 102. When printing ends up to the end of the sheet surface, the carriage returns to the home position and printing is done in the x direction again.
Ink-jet printing apparatuses have recently been used for printing various images. Along with this, the quality of a printed image degrades under specific conditions.
For example, if a plurality of types of inks are discharged onto a printing medium within a short time in a region where black and color images are adjacent to each other, these inks are mixed with each other before absorbed in the printing medium. As a result, color nonuniformity or the like occurs, and the quality of a printed image degrades.
As a method which prevents color nonuniformity of an image, Japanese Patent Laid-Open No. 06-210877 discloses a technique of performing black printing and color printing in different main scanning in a region where black and color images are adjacent to each other, thereby printing a high-quality image free from any color nonuniformity.
In the technique disclosed in Japanese Patent Laid-Open No. 06-210877, a nozzle width used for black printing and a nozzle width used for color printing are set almost equal to each other, and the time lapsed between printing operations is adjusted.
Demands have arisen for a method of preventing degradation of the quality of a printed image by another arrangement when an image having a region where black and color images are adjacent to each other is printed by an ink-jet printing apparatus.
Further, printing disclosed in this reference prolongs the printing time in a case where the number of nozzles (nozzle width) used in color printing is small.